The Holland Tunnel was the longest underwater vehicular tunnel in the world when it opened.

The Holland Tunnel opened in 1927 as the first underwater vehicular crossing of the Hudson River between Manhattan and Jersey City, New Jersey. Once described as the "Eighth Wonder of the World," at the time of completion it was the longest underwater vehicular tunnel, the first tunnel constructed with a ventilation system specifically designed to handle automobile and truck exhaust fumes, and had the largest tube width—twin tubes at 29.5 feet (9 m) in diameter, setting the standard for other vehicular tunnels throughout the world that followed.

Plans for the Hudson River crossing began in 1906 with the appointment of joint commissions in New York and New Jersey to construct one or more bridges between New York City and New Jersey. While initial proposals called for a bridge, J. Vipond Davies (president of the ASCE New York Section in 1921-1922) was an early proponent of a tunnel from Canal Street in Manhattan to 13th Street in Jersey City. In 1913, Davies estimated the cost of a tunnel at $10 million, compared to $50 million for a bridge in the same location. The commissions would later concur that a bridge was not economically feasible due to the long span that would be required to cross the Hudson River, the deep foundations that would be needed to reach bedrock, and the lengthy approaches would necessitate the purchase of large amounts of real estate.

Clifford Milburn Holland was appointed as chief engineer of the tunnel project and began work on June 15, 1919. Although he was just 36 years old, Holland was a well-known expert in underwater tunnel construction, having designed four subway tunnels across the East River including the IRT Clark Street Tunnel (2 and 3 trains), the BMT 14th Street Tunnel (L train), the BMT 60th Street Tunnel (N, R, and W trains), and the BMT Montague Street Tunnel (M and R trains). Educated at Harvard University, Holland received a Bachelor of Arts in 1905 and a Bachelor of Science in Civil Engineering in 1906. He enlisted the help of Ole Singstad to serve as the project's design engineer and Milton M. Freeman to serve as the resident engineer and supervise construction.

The first tunnel with a ventilation system specifically designed for exhaust fumes from motor vehicles, the Holland Tunnel has four ventilation buildings.

Eleven different plans for the tunnel were proposed, including a design by General George W. Goethals (who previously served as chief engineer of the Panama Canal) that included a single tube lined with concrete blocks having two levels, each containing three traffic lanes. Holland's plan called for twin tubes lined with cast iron, each containing two lanes of traffic on a single deck, and was ultimately selected.

Meanwhile, experiments were conducted to provide the data necessary to design the special ventilation system for motor vehicle exhaust. Studies were made in Pittsburgh, Pennsylvania by the Bureau of Mines to determine the composition of motor vehicle exhaust gases, at Yale University to determine the effects of carbon monoxide on humans, and at the University of Illinois to determine the amount of power required to operate the ventilation system. It was concluded that the tunnel's ventilation system would need to keep the carbon monoxide concentration below four parts per 10,000.

Previously, conventional ventilation systems in railroad tunnels were designed to blow air from one portal to the other. This type of longitudinal system would not work in a vehicular tunnel because it would require gale force winds of more than 70 miles per hour (113 km/h) to be blown through the tunnel to clear the exhaust fumes, which would also create a hazard if a fire broke out. Instead, a new type of ventilation system was devised in which clean air would be supplied throughout the tunnel through a fresh air duct located below the roadway with openings at regular intervals. An exhaust duct would be located above the roadway with openings at regular intervals to remove the diluted exhaust fumes out of the tunnel. Thus, air would be drawn straight up within the tunnel, which would confine the spread of flames in the event of a fire.

A 400-foot (122 m) long large-scale model of the tunnel was constructed by the Bureau of Mines near Pittsburgh, Pennsylvania to evaluate the effectiveness of the proposed ventilation system. Clifford Holland also traveled to Europe in 1921 to study the ventilation systems of tunnels in England, Germany, and Scotland. The Holland Tunnel has a total of 84 fans in four ventilation buildings that can completely change the air inside the tunnel every 90 seconds. Electric motors with an output of 6,000 horsepower are needed to drive all of the fans at once, although the tunnel normally operates with some of the ventilation fans shut off and held in reserve.

The Hudson River Vehicular Tunnel was named in memory of chief engineer Clifford Holland, who died two days before the tunnel was holed through.

Construction of the project, then known as the Hudson River Vehicular Tunnel, officially began with a groundbreaking ceremony on March 31, 1922 at the foot of Canal Street in Manhattan. The tunnel was dug out from beneath the riverbed using six shields, each of which was a large cylinder driven by 30 hydraulic jacks with a total force of 6,000 tons (5,400 t). Compressed air was used to pressurize interior of shield to keep out the water and muck; after segments of the tunnel are excavated, 2.5 foot (76 cm) thick cast iron rings are added to support the walls.

Five years into the project, chief engineer Clifford Holland suffered a nervous breakdown as a result of the tremendous stress demanded by the work, having spent long hours working at this desk and in the compressed air of the tubes. He was sent to a sanitarium in Battle Creek, Michigan for rest but died of heart disease on October 27, 1924 at the age of 41. His death occurred just two days before the tunnel was to be holed through, and the celebration that had been planned was canceled in respect for the chief engineer. The two ends of the tubes from New York and New Jersey were joined together without fanfare, even though Holland's mathematical calculations led them to meeting within a fraction of an inch (1 cm) of each other.

Clifford Holland had served as the director of ASCE from 1922 until his death and was one of the twenty members that attended the founding meeting of the ASCE New York Section on February 18, 1920. Following his death in October 1924, President John P. Perry wrote letters on behalf of the ASCE New York Section to both the New York State Bridge and Tunnel Commission and the New Jersey Interstate Bridge and Tunnel Commission asking that the vehicular tunnels under construction be named "The Holland Tunnels." Today, the Holland Tunnel remains one of the few major engineering works that have been named after its engineer. The official proclamation issued by the commissions read as follows:

The Holland Tunnel

At Stated Meetings of the New York State Bridge and Tunnel Commission and the New Jersey Interstate Bridge and Tunnel Commission held Tuesday, November twelfth, nineteen hundred and twenty-four, the following resolution was adopted.

Whereas the untimely death on October twenty seventh, nineteen hundred twenty four of

Clifford Milburn Holland
Chief Engineer in the Construction
of the Hudson River Vehicular Tunnel

has caused a general expression of sorrow; and

Whereas, by comment in the public press as by resolutions of public bodies and societies and expressions from leading citizens and civic organizations, the opinion is general that Mr. Holland gave his life to the work of the planning and construction of this great public utility; and

Whereas, the members of the New York State Bridge and Tunnel Commission and the New Jersey Interstate Bridge and Tunnel Commission are in accord with the widespread suggestion that some fitting attribute be paid to the memory of the deceased Engineer; Therefore be it

Resolved, that the Hudson River Vehicular Tunnel, now being constructed between Canal and Broome Streets in the Borough of Manhattan, City of New York, and 12th and 14th Streets, Jersey City, New Jersey, be and it is hereby dedicated to the memory of Clifford Milburn Holland, and that the said Hudson River Vehicular Tunnel is hereby designated and named as

The Holland Tunnel

Following Clifford Holland's death, Milton H. Freeman took over as chief engineer of the Holland Tunnel but fell ill of acute pneumonia and died on March 24, 1925. He was succeeded by Ole Singstad, who oversaw construction of the Holland Tunnel for the next two and a half years until its completion. Singstad went on to design all of New York City's underwater vehicular tunnels (the Lincoln Tunnel, Queens Midtown Tunnel, and Brooklyn-Battery Tunnel), the Baltimore Harbor Tunnel, and other tunnels abroad. Singstad also served as the president of the ASCE Met Section in 1934-1935.

The Holland Tunnel formally opened on the afternoon of November 12, 1927 when President Calvin Coolidge used a golden telegraph key from his yacht in the Potomac River to part two large American flags draped over the entrances to the tunnel (the same key that was used to explode the final charge on the Panama Canal). Twenty thousand people walked through the tunnel during a two-hour period and viewed the engineering marvel before it was opened to vehicles at midnight. The first car to enter the Holland Tunnel from Manhattan carried chairmen of the New York State Bridge and Tunnel Commission and the widows of Clifford Holland and Milton Freeman. The New York entrance plaza was named Freeman Square in memory of the tunnel's second chief engineer.

ASCE and ASME formally designated the Holland Tunnel as a National Historic Civil and Mechanical Engineering Monument on May 2, 1984.

Stretching 8,557 feet (2,608 m) from portal to portal in the North Tube and 8,371 feet (2,551 m) in the South Tube, the Holland Tunnel cost $48.5 million to build and the expenses were equally shared by states of New York and New Jersey. A total of 5,250 feet (1,600 m) of the tunnel's length is located underwater at a maximum depth of 93.5 feet (28 m) below the surface. The Holland Tunnel relieved traffic strains on ferries crossing the Hudson River, which previously required a transit time of 18 minutes and sometimes required motorists to wait on line for hours. It also facilitated the transport of goods across the Hudson River, which had previously served as a barrier to shipping materials between New Jersey and New York City.

The Port of New York Authority later acquired the Holland Tunnel in 1931 and assumed its operations. Although the opening of the New Jersey Turnpike diverted some of the traffic crossing the Hudson River to the Lincoln Tunnel and George Washington Bridge, the Holland Tunnel continues to remain a vital and heavily patronized crossing between Manhattan and New Jersey. Today, the Holland Tunnel is the second longest continuous underwater vehicular tunnel in North America (after the 9,117-foot [2,779 m] long Brooklyn-Battery Tunnel, which opened in 1950).

The Holland Tunnel was formally designated a National Historic Civil and Mechanical Engineering Landmark on May 2, 1984 at ceremonies attended by officials attended by the two national Societies and the Port Authority of New York & New Jersey. ASCE President S. Russell Stearns and American Society of Mechanical Engineers (ASME) Past-President Donald N. Zwiep joined Port Authority Assistant Executive Director Robert F. Bennett at the New York Plaza of the Holland Tunnel to unveil a commemorative bronze plaque mounted on a five-foot high granite pedestal. Mr. Bennett welcomed guests to the ceremony, at which speakers included Robert A. Olmsted, Chairman of the ASCE Met Section History & Heritage Committee and Dr. Robert B. Gaither, member of the ASME History & Heritage Committee and past-president of the Society. Today, the plaque can be viewed on the west side of Varick Street between Watts and Broome Streets, near the entrance to the north tube of the Holland Tunnel.